The virtual acoustic testing of gear drives has gained growing importance. Fundamentally, the transmission error (TE) is predicted, since it directly affects the vibration and noise characteristics. In this study, the effect of the harmonically distributed tooth microgeometric variations on the TE is investigated via elastic multibody simulations of a helical gear pair. The sensitivity analysis focused on the tip relief, the root relief and the barrelling. The model considered different degrees of linear-, quadratic- and cubic-harmonically distributed variations. The results showed that barrelling with quadratic harmonic micro-geometry had the most significant effect on TE. In addition, if harmonic distributions accidentally coincide in the pairing of the gears, the TE is significantly amplified, leading to a pronounced excitation of the system dynamics.